On 7/19/11 6:02 PM, Brian E Carpenter wrote:
Correct; fragment as if the path mtu was 1280.
But in addition, insert a fragment header even for packets that don't
require fragmentation.
It's always been my understanding that an interface sending IPv6 packets
MUST implement some (unspecified) form of framentation and reassembly
*below layer 3* if the link MTU is less than 1280. In other words a
PTB for a packet of length 1280 is an unrecoverable violation.
>
For example, if you're tunneling IPv6 over an IPv4 network whose PMTU (to
the other end of the tunnel) is, to take a random example, 576, the tunnel
end points could use IPv4 fragmentation and reassembly to provide a 1280 MTU
for the IPv6 traffic.
That would be true for tunneling IPv6 over IPv4.
But the topic was the wording in RFC 2460 that was added to make it
feasible to build (stateless) translators between IPv6 and IPv4.
Of course this doesn't cover the NAT64 case; so what? NAT breaks many things.
We just have to rely on the real world, where the layer 2 link MTU is pretty
much always 1500 today.
We do have language in RFC 2460 to handle this particular case.
Erik
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